Can someone explain this short paragraph concerning wave file analysis (what exactly is the input and output?):

The default input to this program is a text file containing a uniformly sampled

time series, presented as a column of numbers. The default standard output is

the magnitude of the discrete Fourier transform of the input series, normalized

by the length of the FFT.

(If you want to see the code: http://www.physionet.org/physiotools/wfdb/psd/fft.c)